Two Packs, One Boundary

Squeeze an instant cold pack and it plunges to 2 °C. Squeeze a hand warmer and it climbs to 54 °C. Both got a temperature change; only one absorbed energy. Everything about this topic — the words, the sign, the arithmetic — is decided by one question: where did you draw the boundary, and which way did the energy cross it?

8 STEPS · 6 QUICK CHECKS · ΔH_soln(NH₄NO₃) = +25.7 kJ/mol · ΔH_soln(CaCl₂) = −82.8 kJ/mol · v1